The Scanning Desorption Molecule Microscope (SDMM) developed with NIH (Harvard-MIT Biomaterials Program Project) and DoD (Joint Services Electronics Program) support during the last five years will be used to carry out surface studies of tissue and biomaterials with collaboration of investigators both within and outside the Harvard-MIT Biomaterials Program Project Grant. The SDMM uses a focussed electron beam to cause local desorption either by heating or electron stimulated desorption of molecules that are either part of the sample surface or previously applied as a surface stain. In surface studies of materials of physical and chemical interest the binding energy of molecules to the surface is an important parameter, and one of our objectives is to determine these binding energies from point to point on the surface of tissue and biomaterials. Staining techniques in which small molecules are first deposited on the surface and then desorbed will also yield information concerning the composition of the surface. It should thus be possible to obtain new information not otherwise available concerning both chemical composition and chemical function of various parts of the surfaces of biomaterials. Besides using the SDMM in collaboration with other investigators to study and characterize the surfaces on non-thrombogenic materials, erythrocyte ghosts and natural and synthetic membranes, studies will be continued relating to sample preparation, surface staining methods, ion bombardment etching of the surface to remove contaminants and modified freeze-fracture techniques to expose layers beneath the surface, the interpretation of denaturing, and various instrument improvements.